Gliederung

Objective

From a public health point of view, there is growing interest in the epidemiology of impaired cognitive function as a multi-factorial disease, regardless of disease type. Hypertension is known to be a causal factor of cardio-vascular diseases, such as stroke, that can be attenuated by adequate treatment of hypertension [Ref.Â 1]. The results of the few published studies on the role of hypertension, treated and untreated hypertension and cognitive function are inconclusive [Ref.Â 2], [Ref.Â 3], [Ref.Â 4], [Ref.Â 5].

The objective of this analysis was to examine the association between hypertension, with and without treatment, and cognitive function in an ongoing population based cohort study of the elderly.

Research design and Methods

The HeiDE-study („Heidelberger Langzeitstudie zu Risikofaktoren und Diagnose chronischer Erkrankungen“) is an ongoing population-based cohort study. A random sample from Heidelberg and surrounding communities was recruited from 1991 to 1995 (5114 participants; 40-65 years old), and responded to a questionnaire.

All HeiDE participants had a follow-up after approximately 10-years to assess the development of individual health conditions and mortality between baseline and follow-up (2002-2003). From those alive, 4010 (83%) sent back the questionnaire and gave written informed consent for future contact and follow-up.

In 2003, we chose those participants who were 70+ years and had returned the fol-low-up questionnaire (740) to participate in an auxiliary study on cognitive function.

Information on hypertension and on treatment of hypertension was available from the follow-up questionnaire.

We then conducted the telephone interview on cognitive Status (TICS), a validated instrument to assess cognitive function [Ref.Â 6]. It consists of different parts addressing short term and long term memory, prospective memory, and orientation in time and space (41 dichotomous items). Depressive symptoms were measured using the Geriatric Depression Scale (GDS [Ref.Â 7]). The TICS cognitive function score was dichotomized according to the observed distribution at the 25th percentile of values into impaired cognitive function (below 25th percentile) and normal function. Multivariable logistic regression was used to estimate the association between hypertension and impaired cognitive function.

Results

All 740 participants were contacted by mail at least once (100%). Of those still alive (729), 240 (32.9%) refused to participate and 16 (2.2%) could not be reached. The remaining 473 participants (64.9%) gave written informed consent and were interviewed. Differences between non-participants and participants were minor.

Out of 473 participants interviewed, 233 (49.7%) reported a history of hypertension of whom 96 (20.5%) were treated with antihypertensive medications.

Discussion

In this population-based study on cognitive function in the elderly, we observed a self-reported history of hypertension not to be associated with impaired cognitive function irrespective of self-reported antihypertensive treatment.

Our results are in accordance with Scherr et al. who conclude that blood pressure is not a substantial contributor to cognitive function in the elderly [Ref.Â 8]. In contrast, Battersby et al. observed a consistent trend of poorer performance on cognitive function tests in hypertensives [Ref.Â 9]. Prencipe et al. [Ref.Â 10] reported the group of “cognitive impairment no dementia” associated with hypertension (OR 2.3, 95% CI 1.5-35) and the “circumscribed memory impairment” group also associated with hypertension (OR=3.7; 1.7-8.0).

Results which may also explain our findings were recently presented by Waldstein et al. [Ref.Â 5], who found systolic blood pressure nonlinear related to longitudinal change on tests of nonverbal memory and confrontation naming (N=847). Further, cross sectional results indicated moderate U- and J-shaped relations of blood pressure and cognitive function, both high and low blood pressure being associated with poorer cognitive performance on some tests under less-educated participants [Ref.Â 5].

This sets up the question about the optimal level of blood pressure control and the high importance for well controlled blood pressure by antihypertensive medications [Ref.Â 3]. More differentiated blood pressure groups might reveal the association with cognitive impairment and explain the role of antihypertensive treatment.

The strength of our study is the population-based sample. Our study is population based, includes both sexes, a wide range of socio-economic backgrounds, and a broad range of health seeking behavior. Therefore, our results are likely to be generalizable to the general population. Several limitations should be considered. The main limitation of our study is the cross-sectional design. We do not have blood pressure values and the self-reports of hypertension or treatment could lead to misclassification that might not be independent of cognitive function and therefore bias the results towards an inverse association. Not separating different antihypertensive drug classes might obscure effects and class specific analyses will be performed and presented.

Despite these limitations, our study as well as the current evidence from other studies indicate that the association between blood pressure, hypertension, as well as antihypertensive treatment and cognitive function in older age is complex. Hypertension might not be associated with an increased risk for cognitive impairment after control for comorbidity, including stroke.

Acknowledgements

The study was supported by a grant from the German Research Foundation (Graduiertenkolleg 793).